This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-328393 filed on Oct. 23, 2000.
1. Field of the Invention
The present invention relates to a control apparatus used for an internal combustion engine for controlling a fuel-injection volume or an air-fuel ratio.
2. Description of Related Art
A three-way catalyst is installed within an exhaust pipe and used for cleaning exhausted gas. An air-fuel ratio sensor is provided at the upstream side of the three-way catalyst. The fuel-injection amount is adjusted by execution of state feedback control. In detail, the air-fuel ratio of the exhausted gas is controlled to a value in the cleaning window of the catalyst, that is, a value close to a stoichiometric air-fuel ratio, by monitoring a signal output by the air-fuel ratio sensor. By execution of such feedback control, the exhausted gas can be cleaned with a high degree of efficiency. As disclosed in JP-A-7-11995, in the control of the air-fuel ratio, control objects ranging from a fuel injection valve to an air-fuel ratio sensor are modeled, and a feedback gain of a state feedback loop is calculated by using an optimum regulator. The feedback gain is then used for calculating an air-fuel ratio correction coefficient. Finally, a fuel-injection amount is calculated by correction of a basic fuel-injection amount, which is found from the operating conditions of the engine, by using the air-fuel ratio correction coefficient and others.
With the conventional air-fuel ratio control, the feedback gain cannot be changed continuously in accordance with the operating conditions of the engine. Thus, in order to make the control system stabile, control must be executed at a small feedback gain. As a result, the air-fuel ratio control has a shortcoming that the precision of the air-fuel ratio control is poor.
A first object of the present invention is to provide a control apparatus for an internal combustion engine that is capable of varying a control parameter of a feedback control system of the internal combustion engine continuously in accordance with an operating conditions of the engine and capable of improving control precision.
A second object of the present invention is to provide a control apparatus for an internal combustion engine that is capable of calculating a control parameter of a feedback control system of the internal combustion engine in a real-time manner.
In general, an air-fuel ratio correction coefficient FAF (i) is calculated based on control parameters F0 through Fd+1 by using the following equation:
xe2x80x83FAF(i)=F1xc2x7xcex(i)+F2xc2x7FAF(ixe2x88x921)+F3xc2x7FAF(ixe2x88x922)+. . . +Fd+1xc2x7FAF(1xe2x88x92d)+F0xc2x7xcexa3(xcexrefxe2x88x92xcex(i)
where notations xcex(i) denotes the present air-fuel ratio, notations FAF (ixe2x88x921) through FAF (ixe2x88x92d) each denote a previous air-fuel ratio correction coefficient and notation xcexref denotes a target air-fuel ratio or a target air excess ratio.
In this method of calculating the air-fuel ratio correction coefficient, however, when the values of the control parameters F0 through Fd+1 are changed in accordance with operating conditions and the like, the air-fuel ratio correction coefficient FAF is temporarily thrown into confusion at that moment. As a result, it is quite within the bounds of possibility that there occurs a phenomenon of a temporary confusion state of the air-fuel ratio xcex.
In order to solve the problem, the present air-fuel ratio correction coefficient is found by using the following equation:
FAF(i)=FAF(ixe2x88x921)+xcex94FAF(i)
where notation FAF (i) denotes the present air-fuel ratio correction coefficient, notation FAF (ixe2x88x921) denotes the immediately preceding air-fuel ratio correction coefficient and notation xcex94FAF (i) denotes a correction value for correcting the present air-fuel ratio correction coefficient FAF (i). The correction value xcex94FAF (i) is found by a correction value processing means on the basis of a control parameter calculated by a control parameter processing means, an air-fuel ratio change detected by an air-fuel ratio detecting means, a deviation of an actual air-fuel ratio from a target air-fuel ratio and a previous correction value for correcting the air-fuel ratio correction coefficient.
By finding the present air-fuel ratio correction coefficient in this way, the air-fuel ratio correction coefficient is no longer temporarily thrown into confusion even if the values of the control parameters are changed in accordance with operating conditions and the like. Thus, it is out of the bounds of possibility that there occurs a phenomenon of a temporary confusion state of the air-fuel ratio xcex. As a result, stable control of the air-fuel ratio can be executed while the values of the control parameters are being changed in accordance with operating conditions and the like.
Feedback control systems of an internal combustion engine include an idle-operation-speed control system in addition to the air-fuel ratio feedback control system.
According to the present invention, these feedback control systems each comprise a state-detecting means for detecting the state of a control object, a state variation outputting means for outputting present and previous operation amounts as well as present and previous state detection values detected by the state detecting means as a state variable representing an internal state of a control model, and a control parameter processing means for finding a control parameter by using model parameters of the control model. A correction value processing means finds an operation amount correction value based on a difference between a control parameter found by the control parameter processing means, a state variable output by the state variation outputting means, and a deviation of a detection value output by the state-detecting means from a control target value. An operation amount processing means adds the operation amount correction value to a previous operation amount in order to attain a present operation amount.
By finding the present control amount in this way, the state of the control object is no longer temporarily thrown into confusion even if the values of the control parameters of the control object are changed in accordance with operating conditions and the like. As a result, stable control of the control object can be executed while the values of the control parameters are being changed in accordance with operating conditions and the like.